1. Field of the Invention
The present invention relates to a scroll pump which may be effectively used as a compressor for pressurizing a refrigerant in an automobile air-conditioning system.
2. Description of the Related Art
Canadian Pat. No. 567,297 issued Dec. 9, 1958 to John L. Jones and entitled "Scroll Pump" discloses in FIGS. 1 through 3 a scroll pump having a casing provided with a spirally shaped groove called a female scroll. An impeller carrying a fluid displacement means called a male scroll and cooperating with the female scroll is adapted to be oscillated about a fixed axis to perform a pumping action.
In the scroll pump of this nature, the pump capacity may be augmented by increasing the radial dimension of the male and female scroll members or by increasing the axial dimension thereof. The former approach would result in an increase in the size of the pump or compressor and, hence, would fail to meet recent demands for a more compact, light-weight compressor suitable for installation in an automobile. The latter method is hard to follow from a practical point of view, in consideration of the inevitable low productivity that would result from the difficulties arising when attempting to machine male and female scrolls having a large axial length.
Another approach to increasing the compressor capacity is to provide a pumping unit on each side of the impeller, as disclosed in FIG. 4 of the afore-mentioned Canadian patent, each pumping unit comprising a male and a female scroll. In the present specification and appended claims, this structure will occasionally be referred to as the twin-unit type scroll pump. Although this arrangement enables the pump capacity to be twice augmented without increasing the overall radial dimensions, a problem arises in that the twin-unit scroll pump of Jones is not suitable for use as a compressor for a refrigerant because the male and female scrolls extend only through an arc of about 360.degree. so that the output delivery pressure of the pump cannot be brought to a level high enough to effectively operate a vehicle air-conditioning system.
In Japanese Patent Unexamined (Kokai) Publication No. 57-203801 published Dec. 14, 1982 and entitled "Scroll-Type Fluid Machine", with Y. Hattori et al. named as inventors, there is disclosed an oscillating-piston fluid machine wherein similarly-shaped two scroll-type pumping units are provided on both sides of a base plate of the oscillating piston. In each of the pumping units, the male and female scrolls extend, respectively, through two or more spiral turns. This arrangement may be termed a "multiple-stage" fluid machine in the sense that, when the machine is operated as a pump or compressor, the fluid trapped between the male and female scrolls in the outermost or first spiral turn thereof is first compressed to a certain pressure level during the first oscillation of the piston and is then forwarded, in the terminal phase of one complete oscillation of the piston, to the second or subsequent spiral turn of the male and female scrolls wherein the fluid is further compressed to a higher pressure level during the second oscillation of the piston. Thus, when compared with the single-turn or single-stage scroll pump of Jones, the multiple-stage twin-unit scroll machine of Hattori et al., when used as a compressor, is capable of delivering the fluid under a higher pressure, while taking advantage of the twin-unit arrangement.
As illustrated in the drawings of Japanese Patent Publication No. 57-203801, the male and female scroll members extend spirally inwardly and terminate in the vicinity of the central part of the machine. The piston 1 is oscillated by an eccentric shaft 13 coupled to a shaft 2 integral with the oscillating piston. As the piston is oscillated, the respective pumping units operate independently from each other but the outputs from both pumping units are brought together through ports 3 in the piston and are discharged through an outlet 7. To constrain the oscillating movement of the piston with respect to the scroll housing, a bearing 4 is provided having a pin 10 slidably engaged in a circular groove 9. Since the central part of the machine is designed to form the inner end of the groove or female scroll and is not available for accommodating the constraining mechanism 4/9, Hattori et al. provide the constraining mechanism at the peripheral part of the machine. This arrangement suffers from the disadvantage that the radial dimension of the machine is thus increased.
Another example of the twin-unit multiple-stage scroll pump is described in Japanese Patent Unexamined (Kokai) Publication No. 57-171002, published Oct. 21, 1982 and entitled "Scroll-Type Machine", with T. Yuasa et al. named as inventors. In the oscillating piston machine illustrated therein, the male and female scroll members extend through approximately three spiral turns to terminate at the central part of the machine so that, in this area, there is no space available for an eccentric drive and a piston constraining mechanism. Thus, as shown in FIGS. 2 and 3 of that publication, Yuasa et al. provide three circumferentially spaced eccentric/bearing assemblies 6/22 which are arranged along the perimeter of the oscillating piston and are driven by an input shaft 8 through gears 7, 7'. This arrangement necessarily increases the radial size of machine and renders it impossible to provide a compact, light-weight compressor.